For all the international furor over genetically modified food, or GMOs, the biotech industry has really only managed to put a few foreign genes into food crops.

The first of these genes — actually, a small family of similar genes — came from a kind of bacteria called Bacillus thuringiensis, or Bt. Those genes make plants poisonous to certain insect pests.

These genes are a pillar of the entire industry. But that pillar is wobbling. Three of the four Bt genes that are supposed to fend off one particularly important pest, the corn rootworm, are showing signs of failure. Corn rootworms have evolved resistance to them.

But the biotech companies say not to worry. More genes are on the way.

This week, a team of scientists from DuPont Pioneer announced in the journal Science that they'd discovered a new rootworm-killing gene.

They found it by searching through the countless bacteria that live in the soil, looking for one that is lethal to the corn rootworm. Many have carried out such searches and failed. The DuPont Pioneer team, however, succeeded.

They first found a protein that killed rootworms, then worked backward to find the bacteria and the gene that produced that insecticidal protein. Then they inserted the gene into corn plants. As they'd hoped, it worked. The genetically modified corn plants killed rootworms.

"This is a very important discovery, because it shows we can find very efficacious proteins from non-Bt sources," says Tom Greene, a senior research director for DuPont Pioneer.

Meanwhile, Monsanto is working on another new weapon against the rootworm. It relies on a different mechanism, called RNA interference. The modified corn plants produce a type of RNA that poisons rootworms when they eat it.

Despite DuPont Pioneer's discovery, farmers can't celebrate quite yet. Greene says this new weapon against the rootworm won't be available for a decade or so. His company will have to convince regulators that it's safe for people and for the environment.

Fred Gould, co-director of the Genetic Engineering and Society Center at North Carolina State University, says that he hopes that the industry has learned some lessons from the history of the Bt genes. If you overuse a gene like this, it may not work for long.

Years ago, he says, when rootworm-fighting Bt genes were still new, a group of scientists warned the Environmental Protection Agency not to let farmers plant corn containing this gene on all their fields. They predicted that if farmers did so, corn rootworms would evolve resistance to Bt more quickly.

"The majority of the people on that EPA Science Advisory Panel recommended a 50 percent refuge," Gould says. "That means, 50 percent of the corn [seed] that goes out could have the Bt gene, and 50 percent would not."

Seed companies, though, persuaded the government to let farmers plant up to 95 percent of their acres with Bt corn. It encouraged farmers to rely on genetic engineering instead of old-fashioned methods of controlling pests, such as crop rotations — planting their fields with a variety of crops, and not just corn.

It only took about a dozen years for Bt-resistant rootworms to appear.

Gould says that if this new gene eventually does go on sale, he's hoping that regulators manage its use so that it stays effective for longer than the Bt genes have.